Ultrastenos is an extinct genus of Australian mekosuchine crocodilian that lived during the Late Oligocene in northwestern Queensland, Australia. Following its discovery, it was speculated that Ultrastenos was a slender-snouted animal similar to modern gharials or freshwater crocodiles due to the seemingly abruptly narrowing mandible. However, a later study found that this was a missinterpretation of the fossil specimen and that Ultrastenos instead had a more generalized lower jaw. The same publication also provided evidence that the fossils of Ultrastenos belonged to the same animal previously named "Baru" huberi, adding further evidence to the idea that the animal was short snouted, contrary to the initial hypothesis. Given that "Baru" huberi was named first, the type species of Ultrastenos changed from U. willisi to U. huberi in accordance with the rules of the ICZN. Ultrastenos was a small mekosuchine, measuring upwards of 1.5 m (4 ft 11 in) long.
^Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ. 9: e12094. doi:10.7717/peerj.12094. PMC 8428266. PMID 34567843.
and that Ultrastenos instead had a more generalized lower jaw. The same publication also provided evidence that the fossils of Ultrastenos belonged to...
Group. Yates & Stein (2024) interpret Ultrastenos willisi and "Baru" huberi as synonymous, but maintain Ultrastenos as a distinct mekosuchine genus, resulting...
to Baru and instead was a synonym of Ultrastenos willisi, creating the combination Ultrastenos huberi. Ultrastenos is now thought to be closer to Mekosuchus...
this were also recovered by Yates and Stein in their re-evaluation of Ultrastenos and "Baru" huberi. While fossil evidence shows that Mekosuchus originated...
Stein et al. (2018), which recovered it as a more basal form related to Ultrastenos. However, this result has been deemed irregular and was likely caused...
small terrestrial Mekosuchus whitehunterensis, the small semi-aquatic Ultrastenos and the large semi-aquatic Baru wickeni, each likely occupying a different...
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